Di- or polyphase synchronous electric motor with a disc-shaped rotor

ABSTRACT

The stator of this flat magnetized-rotor motor comprises sets of pole pieces, arranged substantially radially, the sets being surrounded by corresponding electrical control coils. Separate yoke portions, having surface portions of axially symmetric design, are arranged in contact with the pole pieces of a corresponding set. The flat portions each consist of two sheet elements, forming between them an angle; the portions are inserted radially in the respective slots of a support portion of a stator element. With this arrangement it is possible to produce high-performance motors, at very low cost and whose dimensions in the radial direction are extremely small.

The present invention is concerned with a di- or polyphase synchronouselectric motor comprising a rotor part shaped as a plane annular disc,magnetized so as to exhibit on each of its plane surfaces at least oneseries of magnetic poles disposed regularly along an annular zone, saidrotor part being integral with a shaft of the motor mounted rotatablywith respect to a stator assembly, this stator assembly comprising atleast two groups of polar parts of a substantially plane configurationdisposed substantially radially with respect to the motor shaft at leaston one side of the rotor part, each of the polar parts forming part of arespective elementary magnetic circuit, having a gap in which isdisposed said rotor part, the stator assembly further comprising atleast two electric control coils, each surrounding at least one of saidgroups of polar parts.

In motors of this type, as they are described for example in theinternational patent application published under No WO 87/03751 or, inanother embodiment, in the Swiss patent No. 637 508, the elementarymagnetic circuits are closed by portions of pieces made by sintering ormade out of sheets of a permeable material, forming the polar parts ofthe stator.

These motors generally have a relatively high cost or price and theyhave outside dimensions which are rather important by comparison withthe diameter of their rotor.

The invention is mainly aimed at remedying this drawback and atproviding a motor, the stator of which is of a particularly simple andinexpensive structure, and the dimensions of which in the radialdirection are reduced to a minimum.

For this purpose, the motor according to the invention has theparticularities indicated in claim 1. Claims 2 to 6 describe preferredembodiments of such a motor.

Other features and advantages of a motor according to the inventionshall become apparent from the description given hereafter, by way ofexample, one embodiment of this motor being illustrated in the appendeddrawing, in which

FIG. 1 is a bottom view of the upper part of the stator assembly of amotor according to the invention, and

FIG. 2 is an axial cross-sectional view of the motor, taken along lineII--II of FIG. 1.

The motor shown in FIGS. 1 and 2 comprises a shaft 1 rotatably mountedin a stator assembly referenced 2, by means of two ball bearings 3 and4. A magnetized annular disc 5 is fixed on an annular part of a rotorsupport 6, the latter being further provided with a tubular part 7,integral with the shaft 1. The disc 5 is magnetized axially so as tohave on each of its faces, along an annular zone, magnetic poles,preferably of alternating polarity, as in the case of the motordescribed in the above-mentioned Swiss patent No 637 508, thefunctioning of which is similar to that of the present motor.

The stator assembly 2 comprises primarily two subassemblies, namely anupper half sector 8 and a lower half stator 9. As shown in particular inFIG. 2, the upper half stator 8 comprises two parts made of a plasticmaterial, 10 and 11, the part 10 comprising, in particular, the supportportions 12 of the polar parts 13, each made of two pieces of a Fe-Sisheet, such as 14 (FIG. 2). The support portions 12 have slots 15accessible axially and the side walls of which are disposed radially.The pieces 14 are inserted into these slots so as to be applied againstsaid side walls and therefore, to be themselves disposed substantiallyradially with respect to the motor shaft. This position and, inparticular, the spacing of the pieces 14 at their outer edge can beensured by a convex portion, such as shown at 16, formed in the slots,on the outer side thereof. Thus, the polar parts 13 have a transversesection corresponding precisely to the configuration of the magneticpoles formed on the disc 5. Similarly, the lower half stator 9 comprisespolar parts, formed by pieces of sheet such as 17 (FIG. 2), disposedopposite the pieces 14, so as to form a gap 18 in which passes themagnetized disc 5.

In the present motor, the pairs of polar parts thus disposed oppositeeach other are arranged in four groups, each group being coupled with arespective electric control coil, from amongst the coils 19, 20, 21, 22,as can be seen in FIG. 1. Each pair of polar parts is part of anelementary magnetic circuit which is closed by a yoke part, common to agroup of pairs of polar parts. Four yoke parts 23, 24, 25, 26 are thusprovided in the present motor.

The yoke parts are, in the present example, formed by pieces of amagnetically permeable sheet, for example made of Fe--Si, these piecesbeing cut out and bent to form parts shaped substantially as portions ofa surface of a revolution cylinder, as shown in FIG. 1, viewed in theaxial direction. Two pieces such as 27, 28 can be disposed one againstthe other in each yoke part and they are maintained together in the twohalf stators 8, 9, as shown in particular in FIG. 2. FIG. 2 furthershows how pieces of sheet, such as 14 and 17, come in contact by theirouter side with the corresponding yoke part 26. During assembly, thepieces 17 and 26 are, for example, disposed in the lower half stator 9,and then the upper half stator 8, into which the pieces 14 had beeninserted, is assembled with the half stator 9. The shape of the piece 14shown in FIG. 2 can facilitate the assembly and ensure the properclosing of the elementary magnetic circuit.

The structure of the yoke of the present motor is much less criticalfrom the standpoint of the dimensional tolerances than a construction inwhich the yoke would consist of a cylindrical tube. The yoke parts canbe made using commercially available sheets, through very simple cuttingand bending operations, the tolerance for the curvature radius beingrelatively high, due to the flexibility of the sheets, while thediametral accuracy of a cylindrical tube implies a relatively high cost.Further, the shown structure enables the construction of a laminatedyoke to be carried out very easily and at a low cost, and ensures a gooddissipation of the heat on the important metallic surfaces which are incontact with the ambient air. Because the magnetic fluxes are directedaxially in the yoke parts, the present structure provides magneticcircuits which are practically independent, thereby enabling theconstruction of motors in which the coils can be used partly as sensorcoils, coils of high-performance di- or tetraphase motors.

I claim:
 1. A polyphase synchronous electric motor comprising a rotorpart shaped as a plane annular disc, magnetized axially so as toexhibit, on each of its plane surfaces at least one series of magneticpoles disposed regularly along an annular zone, said rotor part beingintegral with a shaft of the motor mounted rotatably with respect to astator assembly, this stator assembly comprising at least two groups ofpolar parts of a substantially plane configuration disposedsubstantially radially with respect to the motor shaft at least on oneside of the rotor part, each of the polar parts forming part of arespective elementary magnetic circuit, having a gap in which isdisposed said rotor part, said stator assembly further comprising atleast two electric control coils each surrounding at least one of saidgroups of polar parts, the stator assembly comprising at least twoseparate yoke parts shaped substantially as portions of the surface of arevolution cylinder, each yoke part being disposed in contact with thepolar parts of a group of polar parts, the yoke parts being comprised ofmagnetically permeable pieces of bent sheet material.
 2. A motoraccording to claim 1, wherein the stator assembly comprises statorsupport portions of a non-magnetic material into which are inserted thepolar parts and which support the yoke parts.
 3. A motor according toclaim 1, wherein each elementary magnetic circuit comprises two polarparts disposed opposite each other, substantially in a radial plane ofthe motor on both sides of the rotor part, as well as a portion of ayoke part with which the polar parts are in contact.
 4. A motoraccording to claim 1, wherein each polar part is formed by two pieces ofnon-magnetic sheet, forming between them such an angle that they areeach disposed substantially radially with respect to the motor shaft. 5.A motor according to claim 4, wherein said pieces of sheet are insertedinto a slot of the support portion formed so as to determine the angularposition of each of the two pieces forming a polar part.